In recent years, digital still cameras are rapidly gaining prevalence. Digital still cameras are required to become smaller in size and lower in price, and also to have a high performance. Therefore, recent digital still cameras are equipped with performance-enhancing mechanisms, e.g., a zoom mechanism, an autofocus mechanism, and an optical handshake correction mechanism. However, a camera equipped with these will become large-sized, and cost a lot in production; thus, methods for solving this dilemma are being needed.
FIG. 14 shows lens optics 100 of a commonly-used digital still camera disclosed in Patent Document 1. As shown in FIG. 14, the lens optics 100 are zoom optics, and include a zoom mechanism, a focus adjustment mechanism, and an iris on which an optical handshake correction mechanism, a stop for exposure adjustment, and the like are provided.
The lens optics 100 include a barrel body 101. First, fixed lenses attached to the barrel body 101 will be described. On the barrel body 101, a central fixed lens unit 110 and an imaging-side fixed lens unit 130 are provided. The central fixed lens unit 110 includes a central fixed lens 113, which is fixed to the barrel body 101 by being retained in a central fixed lens holder 111. The imaging-side fixed lens unit 130 includes an imaging-side fixed lens 133 which is fitted into the barrel body 101 while being retained in an imaging-side fixed lens holder 131 and which is fixed by an imaging-side fixed lens retainer 135.
Next, the zoom mechanism will be described. The zoom mechanism includes a zoom main-axis 105M and a zoom sub-axis 105S which are provided on the barrel body 101 and provide guidance when the lens units move. It also includes a first zoom lens unit 150 and a second zoom lens unit 170. The first zoom lens unit 150 includes a first zoom lens 153 and a first zoom lens holder 151 retaining the first zoom lens 153. Similarly, the second zoom lens unit 170 includes a second zoom lens 173 and a second zoom lens holder 171 retaining the second zoom lens 173. A first zoom main-axis receiver 152M and a first zoom sub-axis receiver 152S of the first zoom lens holder 151 are supported on the zoom main-axis 105M and the zoom sub-axis 1055 so as to be capable of moving, whereby the first zoom lens 153 moves along the optical axis (indicated by a shown dot-dash line) direction. Similarly, a second zoom main-axis receiver 172M and a second zoom sub-axis receiver 172S of the second zoom lens holder 171 are supported on the zoom main-axis 105M and the zoom sub-axis 1055 so as to be capable of moving, whereby the second zoom lens 173 moves along the optical axis direction.
Next, the focus adjustment mechanism will be described. The focus adjustment mechanism includes a focus adjustment unit 140 and a focus lens unit 180. The focus adjustment unit 140 includes: a focus adjustment unit main-frame 142M and a focus adjustment unit sub-frame 142S; a focus adjustment unit main-axis receiver 143M and a focus adjustment unit sub-axis receiver 143S which are provided thereon; a focus motor 141; and a focus adjustment lens driving screw 145G. The focus adjustment unit main-axis receiver 143M and the focus adjustment unit sub-axis receiver 143S are supported on the zoom main-axis 105M and the zoom sub-axis 105S, respectively. As the focus motor 141 rotates the focus adjustment lens driving screw 145G in the direction of an arrow DC, the focus adjustment unit main-frame 142M and the focus adjustment unit sub-frame 142S move along the optical axis direction.
The focus lens unit 180 includes a focus adjustment lens holder 181 and a focus adjustment lens 183 which is supported by the focus adjustment lens holder 181. On the focus adjustment lens holder 181, a focus adjustment lens nut 182N and a focus adjustment lens sub-axis receiver 182S are provided. The focus adjustment lens nut 182N is supported so as to be capable of moving along the axial direction while being engaged in a helical groove which is provided in the focus adjustment lens driving screw 145G, and the focus adjustment lens sub-axis receiver 182S is supported by a focus adjustment lens guide 145S which is provided on the focus adjustment unit sub-frame 142S.
A stepping motor being used as the focus motor 141, the focus adjustment mechanism may first detect a terminal position, in a flush state against either moving end, by detecting e.g. an electric current value which increases at that position, and count the number of steps to any moved position therefrom, thus being able to detect a position of the focus adjustment lens 183 along the optical axis direction. Alternatively, this can be detected by an MR device, a hole device, or the like.
Next, the optical handshake correction mechanism will be described. The optical handshake correction mechanism includes an optical handshake correction lens unit 190. The optical handshake correction lens unit 190 includes an optical handshake correction lens holder 191 and an optical handshake correction lens 193 which is retained in the optical handshake correction lens holder 191. The optical handshake correction lens holder 191 is supported so as to be capable of moving relative to the barrel body 101 along an arrow DS1 direction and an arrow DS2 direction (a direction which is orthogonal to the arrow DS1 direction and the optical axis, i.e., a direction which is orthogonal to the plane of the figure), and is driven in the respective directions by a correction first actuator 195a and a correction second actuator 195b. Moreover, the correction first actuator 195a and the correction second actuator 195b are supported respectively on the zoom main-axis 105M and the zoom sub-axis 105S via an optical handshake correction main-axis receiver 192M and an optical handshake correction sub-axis receiver 192S, and thus are capable of moving along the optical axis direction of the lenses.
The amount by which the optical handshake correction mechanism moves the optical handshake correction lens unit 190 is small. Therefore, a hole device can be used for the position detection along the two axes.
For the correction first actuator 195a and the correction second actuator 195b, techniques which are already widely prevalent are used, e.g., a driving force from voice coil-type translatory actuators, or a driving force which is obtained by converting rotary force from a stepping motor into translation by way of screw feeding.
The zoom mechanism includes driving mechanisms and position detecting mechanisms, not shown, for driving the respective lens units along the optical axis direction. The method of driving can be implemented with a construction of realizing predetermined control for actuation by motor-driving an integral cam member which has a cam groove for supporting and guiding each lens holder, a construction of realizing predetermined control for actuation with a motor acting on a screw feed mechanism that is provided for each, or the like.
As the means for detecting the position of any such lens unit along the optical axis direction, an encoder for detecting the movement of a cam member, an MR device, a hole device, or the like can be used.
Because of having a zoom mechanism and a focus adjustment mechanism for moving the lenses along the optical axis direction, and an optical handshake correction mechanism for moving the lenses along biaxial directions which are orthogonal to the optical axis and which are orthogonal to each other, the lens optics 100 having such a construction requires four kinds of driving mechanisms along triaxial directions at the most. Therefore, such a construction makes downsizing and cost reduction of the entire device difficult.